Data Exchange Between Engine Control Module and Other Control Modules With CAN-Bus Interface, Testing
Data Exchange Between Engine Control Module And Other Control Modules With CAN-bus Interface, Testing
NOTE:
- The data exchange between the various control modules is carried out via a data bus.
- The term "CAN-bus" refers to a system for transmitting and distributing data.
- The wires which connect the control modules and convey the data between them are called data wires.
- Data is transmitted via data wires in sequence, i.e. in a specific order to the connected control modules (e.g. engine RPM and accelerator pedal position).
Testing bus system
The DTC table indicates that the data exchange between the engine control module and other control modules with CAN interface should be tested.
- Connect the vehicle diagnostic, testing and information system VAS 5051, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions and select the vehicle system "01 - Engine electronics" from the menu. When doing this the ignition should be switched on.
Display on VAS 5051:
- Select the diagnosis function "08 - Read data block" from the menu -1-
Display on VAS 5051:
1 - Enter display group
(figures up to 255)
NOTE: Data blocks 125 and 126 indicate the control modules which are part of the CAN bus drive.
- Using the keypad -2-, enter "125" to select Display group 125 and confirm entry with Q button.
Display on VAS 5051:
- Check readouts in display zones -1- to -4-.
The display shows the control modules which are equipped with a CAN interface for data transfer with the engine control module.
- No display: control module not equipped with CAN interface
- Display 1: control module with CAN interface forms part of the CAN bus
- Display 0: control module with CAN interface does not form part of the CAN-bus
- Press the Up Arrow button to advance to Display group 126.
- Check readouts in Display group 126 in the same way.
- Press the <- button to exit from the function "08 - Read data block".
Display on VAS 5051:
- Select the diagnosis function "06 - End output" from the menu -1-.
Display on VAS 5051:
- Select the diagnosis function "00 - Check all fault memories" from the menu -1-.
- The Diagnostic Trouble Code (DTC) memory of all on-board systems with self-diagnostic capability will be read.
When a control module answers with its identification the number of stored DTCs appears on the display or "No fault recognized".
Any DTCs that are stored in one of the on-board systems will be displayed one after the other. VAS 5051 will then transmit the next address word.
If DTCs have been stored relating to the "Data bus drive" or "Drive train data bus" or "CAN-bus":
- Check that the engine control module and other control modules with CAN interface are the correct versions for the vehicle (check Part No. and coding).
If the correct control modules are installed:
- Check that multi-pin connectors for control modules are properly seated.
If the multi-pin connectors are properly seated:
- Test CAN bus system.
Testing a "two-wire bus system"
Three or more control modules communicating via a "two-wire bus system"
- Read out the DTCs stored in the control modules.
NOTE: This will help to trace a fault in the wiring.
Example 1:
From the DTCs present in the DTC memories, you can see that control module 1 has no connection to control modules 2 or 3.
Control module Malfunctions present in DTC memory:
1 - No message from control module 2
- No message from control module 3
2 - No message from control module 1
3 - No message from control module 1
- Switch off ignition.
- Disconnect the control modules which are linked by the bus wires and check whether there is an open circuit in one of the bus wires
- If no malfunction can be found in the bus wires replace control module 1.
Example 2:
From the DTCs present in the DTC memories, you can see that control module 2 has no connection to control modules 1 or 3.
Control module Malfunctions present in DTC memory:
1 - No message from control module 2
2 - No message from control module 1
- No message from control module 3
3 - No message from control module 2
- Switch off ignition.
- Disconnect the control modules which are linked by the bus wires and check whether there is an open circuit in one of the bus wires
- If no malfunction can be found in the bus wires replace control module 2.
Example 3:
From the DTCs present in the DTC memories, you can see that none of the control modules are able to transmit or receive signals.
Control module Malfunctions present in DTC memory:
1 - Data bus drive defective
2 - Data bus drive defective
3 - Data bus drive defective
- Switch off ignition.
- Disconnect the control modules which are linked by the bus wires and check for a short circuit to positive or Ground in the bus wires
If the cause of the malfunction "Data bus drive faulty" cannot be found in the data bus wires, check whether one of the control modules is causing the malfunction.
Test requirement:
- Vehicle diagnostic, testing and information system VAS 5051 must be connected and "Vehicle self-diagnosis" selected. Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions
At this stage all the control modules which communicate via the CAN-bus are disconnected. The ignition is switched off.
- Connect one of the control modules.
Display on VAS 5051:
- Switch on ignition.
- Select the relevant vehicle system from menu -1-.
- Check and erase the Diagnostic Trouble Code (DTC) memory of the control module which has just been connected.
- Press the <- button.
- Select the diagnosis function "06 - End output" from the menu -1-.
- Switch the ignition off and then on again.
- Leave the ignition switched on for 10 seconds. Then check the Diagnostic Trouble Code (DTC) memory of the control module that has just been connected, using Scan Tool.
- If the malfunction "Data bus drive faulty" is now indicated, replace the control module which has just been connected.
- If thermal function "Data bus drive faulty" is not indicated, connect the next control module, and repeat the above procedure.